A Note on Abelian Conversion of Constraints

We show that for a system containing a set of general second class constraints which are linear in the phase space variables, the Abelian conversion can be obtained in a closed form and that the first class constraints generate a generalized shift symmetry. We study in detail the example of a general first order Lagrangian and show how the shift symmetry noted in the context of BV quantization arises.Comment: 10 pgs., UR1369, ER40685-81

On the BFFT quantization of first order systems

By using the field-antifield formalism, we show that the method of Batalin, Fradkin, Fradkina and Tyutin to convert Hamiltonian systems submitted to second class constraints introduces compensating fields which do not belong to the BRST cohomology at ghost number one. This assures that the gauge symmetries which arise from the BFFT procedure are not obstructed at quantum level. An example where massive electrodynamics is coupled to chiral fermions is considered. We solve the quantum master equation for the model and show that the respective counterterm has a decisive role in extracting anomalous expectation values associated with the divergence of the Noether chiral current.Comment: 18 pages, LaTeX, no figures, to appear in Journal of Mathematical Physic

Analysis of a chemotaxis system modeling ant foraging

In this paper we analyze a system of PDEs recently introduced in [P. Amorim, {\it Modeling ant foraging: a {chemotaxis} approach with pheromones and trail formation}], in order to describe the dynamics of ant foraging. The system is made of convection-diffusion-reaction equations, and the coupling is driven by chemotaxis mechanisms. We establish the well-posedness for the model, and investigate the regularity issue for a large class of integrable data. Our main focus is on the (physically relevant) two-dimensional case with boundary conditions, where we prove that the solutions remain bounded for all times. The proof involves a series of fine \emph{a priori} estimates in Lebesgue spaces.Comment: 39 page

Remarks on gauge fixing and BRST quantization of noncommutative gauge theories

We consider the BRST gauge fixing procedure of the noncommutative Yang-Mills theory and of the gauged U(N) Proca model. An extended Seiberg-Witten map involving ghosts, antighosts and auxiliary fields for non Abelian gauge theories is studied. We find that the extended map behaves differently for these models. For the Yang-Mills theory in the Lorentz gauge it was not possible to find a map that relates the gauge conditions in the noncommutative and ordinary theories. For the gauged Proca model we found a particular map relating the unitary gauge fixings in both formulations.Comment: 8 pages, no figures. In this revised version, we included the explicit Seiberg Witten maps for antighost and auxiliary fields. We used this expressions to show that it is not possible to relate the Lorentz gauge in noncommutative and ordinary YM theories by the SW map, as claimed in the previous versio

Nonequivalent Seiberg-Witten maps for noncommutative massive U(N) gauge theory

Massive vector fields can be described in a gauge invariant way with the introduction of compensating fields. In the unitary gauge one recovers the original formulation. Although this gauging mechanism can be extended to noncommutative spaces in a straightforward way, non trivial aspects show up when we consider the Seiberg-Witten map. As we show here, only a particular class of its solutions leads to an action that admits the unitary gauge fixing.Comment: General solutions for the map and important reference included, 6 pages, no figure

Development of an energy system for a Mozambique rural village without electric grid access

Tese de mestrado integrado. Engenharia Mecânica (Energia Térmica). Universidade do Porto. Faculdade de Engenharia. 201

Influência do operão nir na adaptação de Staphylococcus aureus às condições do hospedeiro

Staphylococcus aureus is an opportunistic human pathogen, that commensally colonizes the human host and can cause a great number of severe diseases, that can be life-threatening. It is capable of infecting a wide range of tissues, from superficial skin to deeper tissues such as the gastrointestinal track, heart and bones. This variety of tissues show different oxygen concentrations, from highly oxygenated, like blood, to almost anaerobic environments, like the intestines. Little is known of the role played by genes involved in nitrite reduction (NirBD) and siroheme biosynthesis (sirABC) in the adaptation of S. aureus to less oxygenated environments and so it is important to study these genes and the response of this bacteria to the diverse environments found during the host infection. In this work, through qRT-PCR, we observed that oxygen rich environments inhibited the expression of nirR, nirB, sirA and sirC. Hypoxia leads to the onset expression, culminating in higher levels of expression under anaerobic conditions. In anaerobic conditions, nitrates showed to decrease the expression of the nir operon genes and sirC, but their presence also presence improved growth. The mutations ΔnirB, ΔnirD and ΔnirR weaken S. aureus growth, preventing the reduction of nitrites. The deletion of sirC also demonstrated effects, but since the process that is catabolized by this enzyme can occur naturally, but at a lower rate, the effects observed by the deletion of this gene resulted in slightly slower growth and consumption of nitrites, when compared to the wild-type. In summary, S. aureus shows resilience, adapting and surviving, different oxygen environments. It was also showed that the presence of nitrates and oxygen are inhibitors of the expression of the nir and sirC operon genes, in which sirC has been shown to be an enzyme-encoding gene, that when deleted did not impair nitrite reduction by S. aureus.Staphylococcus aureus é patógeno oportunista do ser humano, que coloniza o seu hospedeiro comensalmente, tendo a capacidade de causar diversas doenças, que podem tornar-se mortais. É capaz de infetar uma grande panóplia de tecidos, desde altamente oxigenados, como o sangue, a quase anaeróbicos, como o intestino. Pouco se sabe relativamente ao papel de genes envolvidos na redução de nitritos (NirBD) e síntese de sirohemo (sirABC) na adaptação de S. aureus a ambientes menos oxigenados, sendo por isso importante estudar estes genes e a resposta da bactéria aos diversos ambientes encontrados aquando a infeção do hospedeiro. Neste trabalho, observou-se através de qRT-PCR que ambientes ricos em oxigénio inibem a expressão de nirR, nirB, sirA e sirC. A hipóxia leva ao inicio de expressão destes genes, culminando em superiores níveis de expressão em condições de anaerobiose. Em condições de anaerobiose, nitratos inibem a transcrição de genes do operão nir e sirC, mas a sua presença levou a um maior crescimentos. As mutações ΔnirB, ΔnirD e ΔnirR são debilitadores do crescimento de S. aureus, impedindo a redução de nitritos de uma forma completa. A deleção de sirC, o que resultou num crescimento e redução de nitritos semelhante ao do WT. Em suma, S.aureus, demonstra uma incrível resiliência, adaptandose e sobrevivendo a variadas concentrações de oxigênio. A presença de nitratos e oxigénio são inibidores da expressão dos genes do operão nir e sirC, no qual sirC demonstrou ser um gene que codifica uma enzima que quando deletado não impede a redução de nitritos por parte de S. aureus.Mestrado em Biotecnologi

Hamiltonian formulation of nonAbelian noncommutative gauge theories

We implement the Hamiltonian treatment of a nonAbelian noncommutative gauge theory, considering with some detail the algebraic structure of the noncommutative symmetry group. The first class constraints and Hamiltonian are obtained and their algebra derived, as well as the form of the gauge invariance they impose on the first order action.Comment: enlarged version, 7 pages, RevTe